#REYNOLDS NUMBER AIRFOIL SERIES#

At a chord Reynolds number of 3.2 x 10 6, the maximum lift-to-drag ratio decreases 40% for 140 m roughness, corresponding to a 2.3% loss in annual energy production. Little sensitivity to pressure gradient is observed. The critical roughness Reynolds number varies between 178 to 318, within the historical range. As Reynolds number increases, bypass transition occurs earlier. As distributed roughness height and density increase, lift-curve slope, maximum lift, and lift-to-drag ratio decrease. Results indicate minimal effect from paint-chip roughness. Measurements of lift, drag, pitching moment, and boundary-layer transition were completed. The model chord Reynolds number was varied between 0.8 to 4.8 x 10 6. Distributed roughness was tested in three heights and five density configurations. Insect roughness and paint chips were characterized and recreated moreВ В» as distributed roughness and a forward-facing step. To understand how real-world roughness affects performance, field measurements of turbine-blade roughness were made and simulated on a NACA 63 3-418 airfoil in a wind tunnel.

Furthermore, experiments illustrated distributed roughness is not properly simulated by trip strips. However, roughness was still shown to negatively affect performance. Historically, wind turbine airfoils were designed for lift to be insensitive to roughness by simulating roughness with trip strips. Quantifying deterioration on individual components is difficult, but one potential explanation is accumulation of blade surface roughness. Wind farm operators observe production deficits as machines age. For the unsteady cases, there were increases in the maximum lift and pitching moment coefficient performance for all cases in comparison to the steady state data and a hysteresis behavior due to the oscillating motion. In general, application of leading edge grit roughness reduced the maximum lift coefficient and zero lift pitching moment coefficient and increased the minimum drag coefficient for the steady state data. In addition, the effect of the application of leading edge grit roughness was studied. The airfoils were tested for steady state and for model oscillating conditions having a test matrix which included Reynolds numbers of 0.75 through 1.5 million however, for brevity, only the results for 1 million Reynolds number are included. In a continuing effort to provide experimental data for wind turbine airfoils, tests were conducted at the Ohio State University, Aeronautical and Astronautical Research Laboratory in the 3 X 5 subsonic wind tunnel on the National Renewable Energy Laboratory S814, S812, and S810 airfoil sections. The drag coefficient (with tripping) is significantly affected only at low aspect ratio. The boundary layer tripping is observed to decrease the lift curve slope and stalling angle of attack. The lift coefficient decreases with decreasing thickness ratio, while the drag coefficient increases. The lift and post-stall drag coefficients decrease with decreasing aspect ratio. The pitching moment is unstable beyond stall. The maximum drag coefficient is found to occur at an angle of attack of 90/sup 0/. Both initial and secondary stall are presented.

Results of force and pitching moment measurements, over the angle of attack range, for all combinations of Reynolds numbers, thickness and aspect ratios, and the effects of boundary layer tripping, have been presented. The aspect ratios were 6, 9, 12 and infinity. The thickness ratios studied were 0.18, 0.15, 0.12 and 0.09. Tests were conducted at Reynolds number ranging from one-quarter million to one million.

#REYNOLDS NUMBER AIRFOIL SERIES#

This report documents results of the wind tunnel investigation of constant chord blades moreВ В» having four aspect ratios, with NACA 44XX series airfoil sections, at angles of attack ranging from -10 to 110/sup 0/. The purpose of this wind tunnel study is to characterize the performance characteristics of a blade in stall as a function of its aspect ratio, airfoil thickness and Reynolds number. Peak power predictions upon which wind turbine components are sized depend on a good understanding of a blade's post stall characteristics. Unlike aircraft, a wind turbine's angle of attack range extends deep into stall where the three dimensional performance characteristics of airfoils are not generally known. Wind turbine blades operate over a wide angle of attack range.

Reynolds number airfoil